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Biological Chemistry

Science Concentrates

April 25, 2005 | A version of this story appeared in Volume 83, Issue 17

How plants reward helpful ants

Credit: © SCIENCE 2005

Plants have many enemies, including herbivores, pathogens, and competing vegetation. But they aren't defenseless. By offering nectar as an incentive, plants can recruit animals such as ants to protect them. The interactions between plants and animal mercenaries are shaped by the nature of the nectar. But how do plants control the nectar's chemical composition? And what makes a particular nectar irresistible to one type of ant and unpalatable to another? To answer these questions, Martin Heil of the University of Duisburg-Essen, in Germany, and colleagues studied Acacia plants (Science 2005, 308, 560). Pseudomyrmex ants (shown) that protect the plants are rewarded with nectar. Conceivably, other species of ants that don't do a stitch of defensive work could swoop in and harvest the nectar--but they don't. The researchers learned that the Acacia nectar lacks sucrose, an ingredient favored by many ants, but which Pseudomyrmex ants virtually lack the ability to digest. In fact, the plant apparently employs an as-yet-unidentified enzyme to break down the sucrose it produces in its nectar.

Membrane proteins probed by NMR method

Membrane proteins are difficult to study because they are large and don't crystallize easily. Suzanne R. Kiihne, Huub J. M. de Groot, and coworkers at Leiden University, the Netherlands, and Radboud University, Nijmegen, the Netherlands, describe a new solid-state nuclear magnetic resonance spectroscopy method, called selective interface detection (SIDY), that maps the interactions between a membrane protein and its ligand (J. Am. Chem. Soc. 2005, 127, 5734). The method zeros in on the interactions between 13C on the ligand and protons on the protein. The researchers have studied the interaction of the membrane protein rhodopsin with its ligand 11-cis-retinal as a model system. The method reveals many distant nuclear interactions between the retinal's ionone ring and specific protein residues, which is consistent with other studies showing that the ionone ring is important for selective binding and activation. The results with SIDY, which uses an unlabeled protein from a natural source, are comparable with those obtained in experiments relying on protein isotope labeling based on prior structural knowledge.

Standardization enhances gene-chip reliability

Credit: © SCIENCE 2005
Credit: © SCIENCE 2005

Data collected through a variety of gene-chip technologies may be significantly more reliable and reproducible than currently believed, according to three new studies (Nat. Methods 2005, 2, 337, 345, and 351). Recent comparisons of microarray technologies (gene-chip platforms) showed major inconsistencies among various methods for gene-expression measurement. The results cast doubt across the genetics and disease research communities regarding the usefulness of microarray methods. But now, three methodology studies involving nearly 20 laboratories paint a much brighter picture of gene chip techniques. The investigations were led by research groups at Johns Hopkins University; Dana-Farber Cancer Institute, Boston; and the Toxicogenomics Research Consortium, Research Triangle Park, N.C. According to the studies, the key to reproducibility from lab to lab and across gene chip platforms lies in implementing standardized protocols in every aspect of the investigation, including RNA labeling; hybridization; and data acquisition, filtering, and analysis.

Superlens images the supersmall

With a new "superlens" that can resolve objects only tens of nanometers wide, scientists have finally overcome the long-insurmountable diffraction limit imposed on optical images. The potential applications of such a lens are numerous, from imaging biological samples at unprecedented resolution to dramatically increasing data storage density. Created by Xiang Zhang of the University of California, Berkeley, and colleagues, the superlens can record an image of an entire object in a fraction of a second, unlike atomic force and scanning electron microscopes (Science 2005, 308, 534). Physics dictates that conventional lenses can't resolve objects smaller than the wavelength of light reflected by the object. Zhang's group managed to overcome this limit using a thin silver lens under specific conditions. They use the superlens to record images of 60-nm-wide wires spelling the word "NANO" (shown). Current optical microscopes have a resolution of about 400 nm.

Supersized DNA helix glows

Large-size DNA helices with expanded--and fluorescent--versions of adenine (xA), thymine (xT), guanine (xG), and cytosine (xC) paired to their natural counterparts have been prepared and characterized. Two years ago, Jianmin Gao, Haibo Liu, and Eric T. Kool, at Stanford University, prepared xA and xT and showed that DNAs containing them form helices that are wider and more stable than counterparts formed with the natural bases (C&EN, Nov. 3, 2003, page 12). Early this year, the team prepared xG and xC, completing the set of expanded analogs (J. Org. Chem. 2005, 70, 639). In the latest study, they show that DNAs with the expanded bases, or xDNA, recognize natural DNA and RNA in a sequence-specific manner (Angew. Chem. Int. Ed., published online April 18, 10.1002/anie.200500069). "We have essentially come up with eight new base pairs for a nonnatural form of DNA," Kool says. "To me, it's intriguing that every expanded base of xDNA is fluorescent and that the whole strand might then report--with a fluorescent signal--on its binding to natural DNA or RNA."



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